3C—SiC is often used for microelectromechanical system (MEMS) device structures. 3C—SiC material layers grown on silicon second substrates typically have high residual stress, high dislocation density, and high surface roughness. The 3C—SiC material layers can be grown on silicon second substrates with an (100) orientation surface or an (111) orientation surface. However, there is significant thermal expansion mismatch between the 3C—SiC epitaxial layer and a silicon second substrate, and the 3C—SiC has high built-in strain, many defects, and is typically less than 2 microns thick.
SiC beams have been fabricated using photoelectrochemical selective etching, but the resulting beam thickness has been limited to approximately 1 micron. SiC beams have also been fabricated using hydrogen ion implantation and splitting, but the hydrogen ion implantation limits the SiC beam thickness to approximately 1 micron.
U.S. Pat. No. 6,788,175 is directed to an anchor system for securing a MEMS device to a substrate comprising multiple anchors. A MEMS structure, built in accordance with the one embodiment of the invention, comprises a flexible beam suspended over a substrate and a base attached to each end of the beam. Each base is supported above the substrate by multiple anchors attached to the surface of the substrate. Each anchor further comprises anchor legs along its sides that support the base off of the substrate. In one embodiment, the anchors of each base are located away from the interface between the beam and the base. In another embodiment, the lengths of the anchor legs of the anchors are made longer along a direction of good side-wall step coverage than along a direction of poor side-wall step coverage.
U.S. Pat. No. 6,936,492 is directed to a transducer which comprises an unbalanced proof mass, and which is adapted to sense acceleration in at least two mutually orthogonal directions. The proof mass has first and second opposing sides that are of unequal mass.
U.S. Pat. No. 7,637,160 is directed to a MEMS device that has a sensitivity to a stimulus in at least one sensing direction, which includes a substrate, a movable mass with corner portions suspended in proximity to the substrate, at least one suspension structure coupled approximately to the corner portions of the movable mass for performing a mechanical spring function, and at least one anchor for coupling the substrate to the at least one suspension structure. The at least one anchor is positioned approximately on a center line in the at least one sensing direction.
U.S. Pat. No. 8,499,629 is directed to a mounting system for a MEMS device includes a proof mass selectively coupled to a substrate using a centrally located, single anchor mount that minimizes sensitivity to strain variations experienced by the MEMS device. The mounting system may include isolation cuts arranged in the proof mass to advantageously achieve a desired amount of strain isolation and to produce hinges that extend in opposite directions from the anchor mount. The single anchor mount is arranged to reduce a separation distance from a mid-point or centroid of the anchor mount to its perimeter as compared to conventional mounting schemes that have multiple anchor mounts positioned distally from a common mid-point.
U.S. Pat. No. 8,555,719 is directed to a microelectromechanical systems (MEMS) sensor including a substrate and a suspension anchor formed on a planar surface of the substrate. A first folded torsion spring and a second folded torsion spring interconnect the movable element with the suspension anchor to suspend the movable element above the substrate. The folded torsion springs are each formed from multiple segments that are linked together by bar elements in a serpentine fashion. The folded torsion springs have an equivalent shape and are oriented relative to one another in rotational symmetry about a centroid of the suspension anchor.
U.S. Pat. No. 9,509,278 is directed to a MEMS device including a resonator suspended from a substrate, an anchor disposed at a center of the resonator, a plurality of suspended beams radiating between the anchor and the resonator, a plurality of first electrodes disposed about the anchor, and a plurality of second electrodes disposed about the anchor. The plurality of first electrodes and the resonator form a first electrostatic transducer. The plurality of second electrodes and the resonator form a second electrostatic transducer. The first electrostatic transducer and the second electrostatic transducer are configured to sustain rotational vibrations of the resonator at a predetermined frequency about an axis through the center of the resonator and orthogonal to a plane of the substrate in response to a signal on the first electrode.
U.S. Pat. No. 9,562,926 is directed to a MEMS device including a substrate, a proof mass, a spring, a spring anchor, a first electrode anchor, and a second electrode anchor, a first fixed electrode, and a second fixed electrode. The proof mass is connected to the substrate through the spring and the spring anchor. The proof mass includes a hollow structure inside, and the spring anchor, the first electrode anchor, and the second electrode anchor are located in the hollow structure. The proof mass and the first fixed electrode form a first capacitor, and the proof mass and the second fixed electrode form a second capacitor. There is neither any portion of the proof mass nor any portion of any fixing electrode located between the first electrode anchor, second electrode anchor, and the spring anchor.
The contents of these prior patents are hereby incorporated by reference in their entirety.
The hexagonal SiC electromechanical device structures of the invention, and methods for forming them, beneficially exhibit good thermal expansion matching, and low capacitance. They also provide higher modulus, higher density, superior isoelasticity, improved radiation hardness, higher stiffness, higher fracture toughness, higher shock resistance, and higher thermal conductivity than silicon. This allows the device structures of the invention to achieve well-controlled device characteristics over a range of temperatures, and the electromechanical hexagonal SiC device structures are particularly advantageous in high-gravitational-force (G-force) applications, and in applications requiring radiation hardness.